Nanowire electronic devices and method for producing the same

ABSTRACT

The present invention is directed to an electrical device that comprises a first and a second fiber having a core of thermoelectric material embedded in an electrically insulating material, and a conductor. The first fiber is doped with a first type of impurity, while the second fiber is doped with a second type of impurity. A conductor is coupled to the first fiber to induce current flow between the first and second fibers.

This application is a Divisional of U.S. patent application Ser. No.11/837,364, filed Aug. 10, 2007, which is a continuation-in-part of U.S.patent application Ser. No. 11/301,285, filed Dec. 9, 2005, the entirecontents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention is directed to nano-wire electronic devices andmethods for producing the same.

DESCRIPTION OF THE RELATED ART

Thermoelectric materials generate electricity when subjected to athermal gradient and produce a thermal gradient when electric current ispassed through them. Scientists have been trying to harness practicalthermoelectricity for decades because practical thermoelectricity could,inter alia: (1) replace fluorocarbons used in existing cooling systemssuch as refrigerators and air conditioners; and (2) reduce harmfulemissions during thermal power generation by converting some or most ofthe waste heat into electricity. However, the promise of practicalthermoelectricity has not yet been fulfilled. One problem is that,because of its low efficiency, the industry standard in thermoelectrictechnology cannot be functionally integrated into everyday heating andcooling products and systems.

Bulk form thermoelectric devices such as thermoelectric generators(TEG), thermoelectric refrigerators (TER) and thermoelectric heat pumpsare used for the direct conversion of heat into electricity, or for thedirect conversion of electricity into heat. However, the efficiency ofenergy conversion and/or coefficient of performance of these bulk formthermoelectric devices are considerably lower than those of conventionalreciprocating or rotary heat engines and vapor-compression systems. Inview of these drawbacks and the general immaturity of the technology,bulk form thermoelectric devices have not attained immense popularity.

Early thermoelectric junctions were fashioned from two different metalsor alloys capable of producing a small current when subjected to athermal gradient. A differential voltage is created as heat is carriedacross the junction, thereby converting a portion of the heat intoelectricity. Several junctions can be connected in series to providegreater voltages, connected in parallel to provide increased current, orboth. Modern thermoelectric generators can include numerous junctions inseries, resulting in higher voltages. Such thermoelectric generators canbe manufactured in modular form to provide for parallel connectivity toincrease the amount of generated current.

In 1821, Thomas Johann Seebeck discovered the first thermoelectriceffect, referred to as the Seebeck effect. Seebeck discovered that acompass needle is deflected when placed near a closed loop made of twodissimilar metals, when one of the two junctions is kept at a highertemperature than the other. This established that a voltage differenceis generated when there is a temperature difference between the twojunctions, wherein the voltage difference is dependent on the nature ofthe metals involved. The voltage (or EMF) generated per ° C. thermalgradient is known as Seebeck coefficient.

In 1833, Peltier discovered the second thermoelectric effect, known asthe Peltier effect. Peltier found that temperature changes occur at ajunction of dissimilar metals, whenever an electrical current is causedto flow through the junction. Heat is either absorbed or released at ajunction depending on the direction of the current flow.

Sir William Thomson, later known as Lord Kelvin, discovered a thirdthermoelectric effect called the Thomson effect, which relates to theheating or cooling of a single homogeneous current-carrying conductorsubjected to a temperature gradient. Lord Kelvin also established fourequations (the Kelvin relations) correlating the Seebeck, Peltier andThomson coefficients. In 1911, Altenkirch suggested using the principlesof thermoelectricity for the direct conversion of heat into electricity,or vice versa. He created a theory of thermoelectricity for powergeneration and cooling, wherein the Seebeck coefficient (thermo-power)was required to be as high as possible for best performance. The theoryalso required that the electrical conductivity to be as high aspossible, coupled with a minimal thermal conductivity.

Altenkirch established a criterion to determine the thermopowerconversion efficiency of a material, which he named the power factor(PF). The latter is represented by the equation: PF=S2*σ=S2/ρ, where Sis the Seebeck coefficient or thermo-power, σ is the electricalconductivity and ρ (1/σ) is the electrical resistivity. Altenkirch wasthereby led to establish the equation: Z=S2*σ/k=S2/ρ*k=PF/k, wherein Zis the thermoelectric figure of merit having the dimensions of K−1. Theequation can be rendered dimensionless by multiplying it by the absolutetemperature, T, at which the measurements for S, ρ and k are conductedsuch that the dimensionless thermoelectric figure of merit or ZT factorequals (S2*σ/k)T. It follows that to improve the performance of athermoelectric device the power factor should be increased as much aspossible, whereas k (thermal conductivity) should be decreased as muchas possible.

The ZT factor of a material indicates its thermopower conversionefficiency. Forty years ago, the best ZT factor in existence was about0.6. After four decades of research, commercially available systems arestill limited to ZT values that barely approach 1. It is widelyrecognized that a ZT factor greater than 1 would open the door forthermoelectric power generation to begin supplanting existingpower-generating technologies, traditional home refrigerators, airconditioners, and more. Indeed, a practical thermoelectric technologywith a ZT factor of even 2.0 or more will likely lead to the productionof the next generation of heating and cooling systems. In view of theabove, there exists a need for a method for producing practicalthermoelectric technology that achieves an increased ZT factor of around2.0 or more.

Solid-state thermoelectric coolers and thermoelectric generators innano-structures have recently been shown to be capable of enhancedthermoelectric performance over that of corresponding thermoelectricdevices in bulk form. It has been demonstrated that when certainthermoelectrically active materials (such as PbTe, Bi₂Te₃ and SiGe) arereduced in size to the nanometer scale (typically about 4-100 nm), theZT factor increases dramatically. This increase in ZT has raisedexpectations of utilizing quantum confinement for developing practicalthermoelectric generators and coolers [refrigerators]. A variety ofpromising approaches such as transport and confinement in nanowires andquantum dots, reduction of thermal conductivity in the directionperpendicular to superlattice planes, and optimization of ternary orquaternary chalcogenides and skutterudites have been investigatedrecently. However, these approaches are cost-prohibitive and many of thematerials cannot be manufactured in significant amounts.

The ability to efficiently convert energy between different forms is oneof the most recognizable symbols of advances in science and engineering.Conversion of thermal energy to electrical power is the hallmark of theenergy economy, where even marginal improvements in efficiency andconversion methods can have enormous impact on monetary savings, energyreserves, and environmental effects. Similarly, electromechanical energyconversion lies at the heart of many modern machines. In view of thecontinuing quest for miniaturization of electronic circuitry, nanoscaledevices can play a role in energy conversion and also in the developmentof cooling technology of microelectronic circuitry where a large amountof heat is generated. Accordingly, there exists a need for a broadspectrum of high performance energy conversion and thermoelectricdevices, based on one-dimensional inorganic nanostructures or nanowires.

BRIEF SUMMARY OF EMBODIMENTS OF THE INVENTION

The present invention pertains to an electrical device that comprises: afiber having a core of thermoelectric material embedded in an insulatingmaterial; and one or more conductors coupled to one of the fiberportions to induce current flow between the first and second fiberportions. The thermoelectric core has an n-doped portion and a p-dopedportion.

In an embodiment, the thermoelectric core has a width substantiallyequivalent to a width of a single crystal of the thermoelectricmaterial. Additionally, crystals in the thermoelectric core havesubstantially the same crystals orientation.

In a further embodiment, the electrical device is an FET that comprises:a second n-doped portion, wherein the p-doped portion is between thefirst and second n-doped portions; and an insulating layer locatedbetween the p-doped portion and the conductor.

In yet another embodiment, the electrical device is an FET thatcomprises: a second p-doped portion, wherein the n-doped portion isbetween the first and second p-doped portions; and an insulating layerlocated between the n-doped portion and the conductor.

In a further embodiment, the insulating material is selected from thegroup consisting of: pyrex; borosilcate; aluminosilicate; quartz; leadtelluride-silicate; and combinations thereof. The thermoelectricmaterial is selected from the group consisting of: Bi₂Te₃; SiGe; andZnSb. Alternatively, the thermoelectric material comprises PbTe.

In yet another embodiment, the electrical device is an LED or a PV cell.

Other features and aspects of the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings, which illustrate, by way of example, the featuresin accordance with embodiments of the invention. The summary is notintended to limit the scope of the invention, which is defined solely bythe claims attached hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention, in accordance with one or more variousembodiments, is described in detail with reference to the followingfigures. The drawings are provided for purposes of illustration only andmerely depict typical or example embodiments of the invention. Thesedrawings are provided to facilitate the reader's understanding of theinvention and shall not be considered limiting of the breadth, scope, orapplicability of the invention. It should be noted that for clarity andease of illustration these drawings are not necessarily made to scale.

FIG. 1 is a cross-sectional view of a tubular furnace for drawing athermoelectrically active material embedded in a glass cladding, inaccordance with the principles of the present invention;

FIG. 2 is an x-ray diffraction pattern of a PbTe-based cable constructedin accordance with the principles of the invention;

FIG. 3 is a side view of a glass-clad PbTe-based cable constructed inaccordance with the principles of the invention;

FIG. 4 is an enlarged cross-sectional view of the glass-clad PbTe-basedcable of FIG. 3 taken along line 3A-3A;

FIG. 5 is a cross-sectional view of the glass-clad PbTe-based cable ofFIG. 3 after a second drawing of the PbTe fibers;

FIG. 6 is a cross-sectional view of the glass-clad PbTe-based cable ofFIG. 3 after a third drawing of the PbTe fibers;

FIG. 7 is a chart illustrating the DC resistance of the PbTe cable ofFIG. 4 (after a first drawing of the PbTe fibers);

FIG. 8 is a chart illustrating the DC resistance of a PbTe cable of FIG.5 (after a second drawing of the PbTe fibers);

FIG. 9 is a chart illustrating the DC resistance of a PbTe cable of FIG.6 (after a third drawing of the PbTe fibers);

FIG. 10 illustrates a conventional metal oxide field effect transistor(MOSFET);

FIG. 11 illustrates a conventional diode;

FIGS. 12-13 illustrate exemplary nanowire MOSFETs according toembodiments of the present invention;

FIG. 14 illustrates an exemplary nanowire diode according to anembodiment of the present invention; and

FIG. 15 illustrates an exemplary nanowire photovoltaic cell according toan embodiment of the present invention.

The figures are not intended to be exhaustive or to limit the inventionto the precise form disclosed. It should be understood that theinvention can be practiced with modification and alteration, and thatthe invention be limited only by the claims and the equivalents thereof.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

In the following paragraphs, the present invention will be described indetail by way of example with reference to the attached drawings.Throughout this description, the preferred embodiment and examples shownshould be considered as exemplars, rather than as limitations on thepresent invention. As used herein, the “present invention” refers to anyone of the embodiments of the invention described herein, and anyequivalents. Furthermore, reference to various feature(s) of the“present invention” throughout this document does not mean that allclaimed embodiments or methods must include the referenced feature(s).

1.0 DEFINITIONS

Before starting a description of the Figures, some terms will now bedefined.

Bulk Material: Macroscopic-sized thermoelectric materials that aretypically larger than 1 micron or 1 micrometer in all three dimensions.

Chalcogenides: Group VI elements of the periodic table.

Chemical Vapor Deposition: Deposition of thin films (usuallydielectrics/insulators) on wafer substrates by placing the wafers in amixture of gases, which react at the surface of the wafers. This can bedone at medium to high temperature in a furnace, or in a reactor inwhich the wafers are heated but the walls of the reactor are not. Plasmaenhanced chemical vapor deposition avoids the need for a hightemperature by exciting the reactant gases into a plasma.

Doping: Deliberately adding a very small amount of foreign substance toan otherwise very pure semiconductor crystal. These added impuritiesgive the semiconductor an excess of conducting electrons or an excess ofconducting holes (the absence of conducting electrons).

Efficiency: Efficiency is the power generated by a system divided by thepower fed into it, a measure of how well a material converts one form ofenergy into another. Efficiency stands at a mere 8 to 12% for bulk formthermoelectric devices that are currently available or on the nearhorizon.

Figure of Merit: The thermoelectric figure of merit, ZT, is given byZT=(S2*σ/k)*T, where S is the Seebeck coefficient, T is the absolutetemperature, σ is the electrical resistivity, and k is the thermalconductivity.

Lead Telluride: PbTe is one of the most commonly used thermoelectricmaterial other than Bi₂Te₃. PbTe is typically used for power generationbecause this material exhibits its highest ZT at temperatures between400 and 500° C. and has an effective operating range of about 200° C.around 500° C.

Nano: A prefix meaning one-billionth, or 0.000000001. For example, thewavelength of the ultraviolet light used to etch silicon chips is a fewhundred nanometers. The symbol for nanometer is nm.

Quantum Confinement: Quantum Confinement takes place when carriers ofelectricity (electrons or holes) are confined in space by reducing thesize of the conductor. For example, a very thin conducting film reducesthe freedom of a carrier by limiting its freedom to propagate in adirection perpendicular to the plane of the film. The film is said to bea 2-d structure and the carrier in such a film is said to be quantumconfined in one direction. It can move around in two other directions,i.e., in the plane of the film.

Seebeck Coefficient: The electromotive force generated in a materialwhen it is subjected to a thermal gradient and is normally expressed asmicrovolts per Kelvin. The thermoelectric power, or Seebeck coefficient,of a material has a large role in determining its ZT factor.

Thermal Conductivity: Thermal conductivity is an inherent property of amaterial that specifies the amount of heat transferred through amaterial of unit cross-section and unit thickness for unit temperaturegradient. Though thermal conductivity is an intrinsic property of amedium, it depends on the measurement temperature. The thermalconductivity of air is about 50% greater than that of water vapor,whereas the thermal conductivity of liquid water is about 25 times thatof air. Thermal conductivities of solids, especially metals, arethousands of times greater than that of air.

The present invention is directed to nanostructures referred to hereinas “nanowires”, “cables”, “arrays”, “heterostructures” or “composites”that contain a plurality of one-dimensional fibers. Nanowires inaccordance with the present invention generally compriseheterostructures of at least one thermoelectrically active material andone other compositionally and structurally different material (e.g.,glass), wherein an interface or junction is formed therebetween. Thethermoelectrically active material is reduced in thickness or diameterto nano-dimensions in order to harness the advantages of quantumconfinement. In this manner, the thermoelectric efficiency of thethermoelectrically active material is enhanced. The thermoelectricallyactive material is also referred to herein as the “thermoelectricmaterial”. The cladding material preferably comprises a suitable glasssuch as a glass comprising an amorphous material having no long rangeordering of its constituent atoms.

2.0 NANOWIRE

2.1 Overview

A method for producing nanowires capable of exhibiting high ZT values isdescribed herein according to an embodiment of the present invention.The enhanced physical performance and properties of the nanowire may beon account of one or more of the following effects or properties:quantum confinement of carriers; less physical defects such as vacanciesand/or dislocations; reduced grain boundaries; single crystal formation;and favorable orientation of grains. As mentioned, the equation for thethermoelectric figure of merit, Z, can be rendered dimensionless bymultiplying it by an absolute temperature, T, such as the temperature ofthe hot junction of the thermoelectric device. It follows that thedimensionless thermoelectric figure of merit, ZT=(S2*σ/k)*T, can be usedin the evaluation of the performance and energy conversion efficiency,of any thermoelectric material or device.

For nanowires of PbTe, if the bulk thermal conductivity (k) of PbTe isconsidered, the ZT factor at 750 K is still very high (i.e., ZT ofaround 2.0 or more) using ZT=(S2*σ/k)*T. ZT factors increase withtemperatures between about 300 K and 750 K. For PbTe-basedthermoelectric nanowires, the value of S2*σ tends to peak at a certainlevel with the ZT factors increasing with decreasing nanowire width.However, after a certain nanowire width is reached, ZT factors begin tofall with decreasing nanowire width. The PbTe-based nanowires describedherein may be easily tailored to exhibit n-type or p-type conduction,either by changing the stoichiometry of Pb and Te or by adding someminor components/impurities.

Numerous thermoelectric materials, including PbTe, are sensitive tooxygen, which can degrade thermoelectric performance. For this reason,it is advantageous to have such thermoelectric materials sealed off andprotected from oxygen contamination within the target environment range.Of course, a thermoelectric device is not commercially viable if itcannot withstand the elements and environment it is intended to functionunder.

Although PbTe is the preferred thermoelectric material, otherthermoelectric materials may be employed, such as Bi₂Te₃, SiGe, ZnSb,and Cd₈Sb₃, without departing from the scope of the present invention.The thermoelectric material may initially be in any convenient form,such as granules or powder.

Once fiber-drawn nanowire cables were produced using the methodsdescribed above, the electrical conductivity (σ) and thermoelectricpower (S) were measured and the variation of the parameter, S2*σ, wasdetermined. The parameter, S2*σ, is determined experimentally,multiplied by the measurement temperature (in K) and divided by theknown thermal conductivity (k) to provide the ZT values of the nanowiresproduced by the present invention.

Testing of the glass cladding without embedded nanowires using the vander Pauw 4-probe instrument showed that the sample was very resistivesuch that the instrument did not measure any conductivity. Similarly,the measurement of thermopower using a conventional method (e.g. byemploying the Seebeck coefficient determination system, marketed by MMRTechnologies, Mountain View, Calif.) did not produce any result onaccount of the high resistivity of the glass cladding. However, theelectrical conductivity and thermoelectric power of PbTe-embedded cableswas readily measurable, indicating that the measured values ofelectrical conductivity and thermoelectric power are attributable to thecontinuous nanowires along the length of the cable.

The preferred thermoelectric material for the nanowire cables of thepresent invention is PbTe because of its advantageous thermoelectricproperties and reasonable cost. Using the known bulk thermalconductivity value for PbTe, the calculated ZT ((S2*σ/k)*T) factor at750 K is >2.5. The S2σ of PbTe exhibits a definite tendency to peak at acertain nanowire width. Given that the best known ZT factors for bulkPbTe is around 0.5, the resultant ZT factors of around 2.0 or more isconsidered to be significantly enhanced by one or more of quantumconfinement of carriers, less physical defects such as vacancies and/ordislocations, reduced grain boundaries, single crystal formation, andfavorable orientation of grains. The ZT factor increases with decreasingnanowire width until this maximum value is reached, and then the ZTfactor begins to decrease with further decrease in nanowire width. Aswould be appreciated by those of skill in the art, other thermoelectricmaterials having suitable thermoelectric properties (e.g., Bi₂Te₃) maybe employed without departing from the scope of the invention.

In accordance with the present invention, a maximum diameter of thenanowires is preferably less than approximately 200 nm, most preferablybetween approximately 5 nm and approximately 100 nm. In cases where thecross-section of the nanowires is not circular, the term “diameter” inthis context refers to the average of the lengths of the major and minoraxis of the cross-section of the nanowires, with the plane being normalto the longitudinal axis of the nanowires. Nanowires having diameters ofapproximately 50 nm to approximately 100 nm that may be prepared using amethod of drawing of a thermoelectric material in glass cladding, asdescribed hereinbelow.

The cables of the present invention preferably are manufactured toexhibit a high uniformity in diameter from end to end. According to someembodiments of the invention, the maximum diameter of the glass claddingmay vary in a range of less than approximately 10% over the length ofthe cable. For less precise applications, the diameter of the nanowiresmay vary in a larger range (e.g., 5-500 nm, depending on theapplication). Electrically, the glass is preferably several orders ofmagnitude more resistive than the thermoelectric material it is employedto clad. The cables are generally based on a semiconducting wire,wherein the doping and composition of the wire is primarily controlledby changing the composition of the thermoelectric material to yield awire that exhibits either p-type or an n-type thermoelectric behavior.The Cables may be used to develop superior thermoelectric devices in acost-effective manner.

According to the invention, a method of drawing a thermoelectricmaterial in glass cladding involves drawing the glass-cladthermoelectric material to form individual fibers (or monofibers) ofthermoelectric materials, which are preferably about 500 microns indiameter or less. As would be appreciated by those of ordinary skill inthe art, the monofibers may have diameters greater than 500 micronswithout departing from the scope of the invention. Cable diameters maybe brought down to 5-100 nm by repeatedly drawing fiber bundles ofmonofibers, and the concentration of wires in a cross-section of thecable may be increased to ˜109/cm² or greater. Such cables exhibit oneor more of the following effects or properties: quantum confinement ofcarriers, reduced physical defects such as vacancies and/ordislocations, reduced grain boundaries, single crystal formation, andfavorable orientation of grains for providing enhanced thermopowergeneration efficiency.

The method of drawing a thermoelectric material in glass cladding mayfurther comprise bunching the cable together and redrawing several timesin succession to produce a multi-core cable comprising glass-cladthermoelectric fibers. By way of example, the material to forming thefibers of a cable may comprise PbTe or Bi₂Te₃. The resulting cablecomprises a multi-core cable having a plurality of individual fibersthat are insulated from each other by the glass cladding. A particularglass cladding may be chosen to contain a specific composition to matchthe physical, chemical, thermal and mechanical properties of a selectedthermoelectric material. The glass cladding is preferably several ordersof magnitude higher in electrical resistivity than the metal, alloy orsemiconductor material that forms the thermoelectric fibers. Suitablecommercial glasses for most applications include, but are not limitedto, pyrex, vycor and quartz glass.

According to a further embodiment of the invention, the metal, alloy orsemiconductor material that forms the fibers is varied to render a cableeither n-type or p-type, such that individual cables may be used as then-type and p-type components of a thermoelectric device. The cables maybe induced to exhibit one or more of quantum confinement, reducedphysical defects, reduced grain boundaries, single crystal formation,and favorable orientation of grains by reducing the thickness or thediameter of the fibers to a predetermined range, thereby increasing theefficiency of thermopower generation.

2.2 Method of Producing Nanowires

Referring to FIG. 1, vertical tube furnace 10 is employed to provideheat for drawing glass-clad thermoelectric fibers. In particular,vertical tube furnace 10 includes a central lumen 11 for receiving apreform 12 comprising a glass tube 14 that is sealed at an area ofreduced cross-section 18 to form vacuum space 20 that is at leastpartially filled with thermoelectric material 22. The furnace is used tomelt the thermoelectric material 22 and glass tube 14 in preparation forone or more drawing operations for producing glass-clad thermoelectricfibers 24.

With further reference to FIG. 1, vertical tube furnace 10 comprisesfurnace shroud 26, thermal insulation 28 and muffler tube 30. Suitablematerials for muffler tube 30 include conductive metals such asaluminum. Vertical tube furnace 10 further comprises one or more heatercoils 34 embedded therein. More precisely, heater coils 34 are disposedbetween muffler tube 30 and thermal insulation 28, and refractory cement38 is disposed between heater coils 34 and thermal insulation to directthe heat produced by heater coils 34 inwardly to form a hot zone 40within muffler tube 30. Heater coils 34 are provided with leads 44 thatmay be insulated using a ceramic insulator 48. Additionally, athermocouple probe 50 is provided for measuring the temperature withinhot zone 40, which may include a length of approximately one inch.

A method of drawing a thermoelectrically active material 22 comprisingan array of metal, alloy or semiconductor rods embedded in a glasscladding will now be described. Initially, a suitable thermoelectricmaterial 22 is selected. The preferred thermoelectric material of thepresent invention comprises PbTe that is initially in granular form.Additional suitable thermoelectric materials include, but are notlimited to, Bi₂Te₃, SiGe and ZnSb. The next step involves selecting asuitable material for forming the glass tubing 14. The glass materialpreferably is selected to have a fiber drawing temperature range that isslightly greater than the melting temperature of the thermoelectricmaterial (e.g., ≧1120° C. for PbTe). Vertical tubular furnace 10 is thenemployed to seal off one end of glass tubing 14. Alternatively, ablowtorch or other heating device may be used to seal off the glasstubing 14 and create vacuum space 20.

After sealing off one end of the glass tubing 14, the next steps involveintroducing the thermoelectric granules inside the vacuum space 20 andevacuating the tube by attaching the open end of the glass tube to avacuum pump. While the vacuum pump is on, an intermediate portion of theglass tubing 14 is heated such that the glass partially melts andcollapses under the vacuum. The partially melted glass tube provides anampoule 54 containing the thermoelectric material 22 to be used in afirst drawing operation. The next step involves introducing the end ofampoule 54 containing the thermoelectric material 22 into the verticaltube furnace 10. In the illustrated embodiment, the tubular furnace 10is configured such that the ampoule 54 is introduced vertically, whereinthe end of the ampoule 54 containing the thermoelectric granules isdisposed within hot zone 40 adjacent to heater coils 34.

Once the ampoule 54 is properly disposed in vertical tube furnace 10,the temperature is increased such that the glass encasing thethermoelectric granules melts just enough for it to be drawn, as is donein a conventional glass draw-tower, which is per se known in the art. Asdiscussed hereinabove, the composition of the glass is preferably chosensuch that the fiber drawing temperature range is slightly greater thanthe melting point of the thermoelectric granules. For example, if PbTeis selected as the thermoelectric material, pyrex glass is a suitablematerial for drawing the glass with PbTe fibers embedded therein. Thephysical, mechanical and thermal properties of glass tubing 14 andthermoelectric material 22 will have a bearing on the properties of theresulting cables. Glasses exhibiting a minimal deviation of theseproperties with respect to those of the thermoelectric material 22 arepreferably chosen as the cladding material.

The above-described glass tubing 14 may comprise commercially availablepyrex tubing having a 7 mm outside diameter and a 2.75 mm insidediameter, wherein the tube is filled with PbTe granules over a length ofabout 3.5 inches. Evacuation of glass tubing 14 may be achievedovernight under a vacuum of approximately 30 mtorr. After evacuation,the section of glass tubing 14 containing the thermoelectric material 22is heated gently with a torch for several minutes to remove someresidual gas, and then the glass tubing 14 is sealed under vacuum abovethe level of thermoelectric material 22.

In operation, vertical tube furnace 10 is used for drawing theglass-clad thermoelectric fibers. Vertical tube furnace 10 includes ashort hot zone 40 of about 1 inch, wherein the preform 12 is placed inthe vertical tube furnace 10 with the end of the tube slightly below hotzone 40. With the furnace at about 1030° C., the weight from the lowertube end is sufficient to cause glass tubing 14 to extend under its ownweight. When the lower end of glass tubing 14 appears at the loweropening of the furnace, it may be grasped with tongs for hand pulling.Preform 10 may be manually advanced periodically to replenish thepreform material being used up during the fiber drawing process. Fiber24 preferably includes a diameter between about 70 microns and about 200microns. According to additional embodiments of the present invention,the drawing operation may be performed using an automatic draw-towerthat results in very little variation in diameter.

According to further embodiments of the invention, short fiber sectionsmay be formed by drawing the heterostructures and then breaking orcutting the heterostructures into shorter pieces. By way of example,these shorter pieces may be machined to be approximately 3 inches inlength. The pieces are then bundled inside another pyrex tube, which issealed at one end using the vertical tube furnace or using a blowtorch,as described hereinabove. When a suitable number of monofibers arepacked in the tube, the open end is attached to a vacuum pump and anintermediate section is heated. This heating causes the glass tube tocollapse, thereby sealing the tube and forming an ampoule for a seconddrawing operation, which produces a cable having a plurality ofmulti-core fibers. After the second drawing operation, the fibers arecollected and placed in the bore of yet another sealed tube. When thebore is filled with a suitable number of monofibers, the preform isevacuated and sealed under vacuum. Fiber drawing is then performed onthe twice-drawn fibers. This process is repeated as needed to obtain afinal thermoelectric material diameter of about 100 nm.

2.3 Nanowire Structures and Properties

In order to characterize the electronic properties of bulk andheterostructure nanowires, it is important to determine the x-raydiffraction characteristics of the glass-clad thermoelectric material.FIG. 2 depicts an x-ray diffraction pattern of a PbTe-based cableconstructed in accordance with the principles of the present invention,wherein the characteristic spectrum of PbTe is overlaid on a glassyx-ray diffraction pattern. In particular, the x-ray diffraction patternclearly indicates the presence of PbTe peaks and a lack of other peaks,thus illustrating that the glass material has neither reacted with PbTenor devitrified during fiber drawing. These peaks are exclusivelycharacteristic to those of PbTe crystals.

FIG. 3 depicts a glass-clad PbTe-based cable 60 constructed using themethod of drawing a thermoelectrically active material embedded in aglass cladding described hereinabove. Specifically, the cable 60comprises a plurality of multiple monofibers 64 that are bundled andfused to form a cable (or button) of virtually any length. This buttoncan be broken, cut or otherwise sectioned to produce a plurality ofshorter cables having a predetermined length. FIG. 4 is an enlargedcross-sectional view of the glass-clad PbTe-based cable 60 of FIG. 3taken along line 3A-3A. Cable 60 includes a plurality of monofibers 64,has a width of approximately 5.2 mm, and was produced using a singledrawing of the PbTe fibers at a temperature of approximately 300 K.

According to the preferred embodiment of the invention the cable 60 isbunched together and redrawn several times in succession to produce amulti-core cable having a plurality of individual thermoelectric fibersthat are insulated from each other by the glass cladding. FIG. 5 is across-sectional view of the glass-clad PbTe-based cable 60 after asecond drawing of the PbTe fibers. The twice-drawn cable has a width ofapproximately 2.78 mm. FIG. 6 is a cross-sectional view of theglass-clad PbTe based cable 60 after a third drawing of the PbTe fibers,wherein the cable has a width of approximately 2.09 mm.

A multi-core cable having a plurality of thermoelectric fibers isprovided according to an embodiment of the present invention. The cableis similarly produced as cable 60. In the cable, one fiber is made witha different thermoelectric material than the material that made up ofanother fiber. In an embodiment, the thermoelectric fiber is made withp-doped thermoelectric material, and another thermoelectric fiber ismade with n-doped thermoelectric material. Similar to cable 60, thecable is made by fusing a plurality of multiple monofibers prior to asubsequent drawing process. However, instead of using the samemonofibers as with the case with cable 60, monofibers used to create thecable comprises two or more types of thermoelectric materials. Forexample, one strand of monofiber may be p-doped with an acceptor dopantsuch as boron and another monofiber may be n-doped. In this way, thecable will have a combination of n-doped and p-doped monofibers.

The cable may also be broken or sectioned to produce a plurality ofshorter cables, which may be re-bundled and redrawn to produce a cablehaving a desired diameter.

FIGS. 3-6 illustrate the development of microstructure as theconcentration of wires in the cable increases to ˜109/cm2. Thesemicrostructures may be observed using optical and scanning electronmicroscopes. By way of example, energy dispersive spectroscopy may beemployed to unambiguously indicate the presence of PbTe wires in theglass matrix.

2.4 Thermoelectric Property Characterization

An embodiment of the present invention involves the continuity andelectrical connectivity of the glass embedded fibers along the entirelength of the cable. Electrical connectivity is easily demonstrated bydetermining the resistance of the cable at different thicknesses.According to a preferred implementation of the invention, the resistanceof the glass cladding, without any thermoelectric wires embeddedtherein, is about 7 to 8 orders of magnitude higher than that of thecontinuous thermoelectric fibers.

The samples used to determine electrical connectivity of thethermoelectric wires are in the form of “buttons” of PbTe prepared fromthe preforms following the one of the fiber drawing steps. Referring toFIGS. 7-9, the resistance of the thermoelectric wires embedded in theglass is approximately 1 ohm or less. On the other hand, the resistanceof the glass cladding without thermoelectric wires is more than 108ohms, which is about 8 orders of magnitude higher than that of thePbTe-embedded cables. This difference in electrical resistance indicatesthat the glass-clad thermoelectric wires drawn using the methodsdescribed herein exhibit electrical connectivity from one end to theother.

FIG. 7 is a chart illustrating the DC resistance of PbTe cable 60 afterthe first drawing of the PbTe fibers, wherein the resistance of thecable (Ohms) is plotted against the electrical current (amps). Inparticular, the DC resistance of the cable 60 steadily decreases with anincreasing current. FIG. 8 is a chart illustrating the DC resistance ofthe cable 60 after the second drawing of the PbTe fibers, while FIG. 9is a chart illustrating the DC resistance of the PbTe cable 60 after thethird drawing of the PbTe fibers.

A preferred cable produced in accordance with the principles of thepresent invention preferably comprises at least one thermoelectric fiberembedded in an electrically insulating material, wherein thethermoelectric material exhibits one or more of quantum confinement ofcarriers, reduced physical defects such as vacancies and/ordislocations, reduced grain boundaries, single crystal formation, andfavorable orientation of grains. According to the preferred embodimentof the invention, a width of each fiber is substantially equivalent to awidth of a single crystal of the thermoelectric material, wherein eachfiber has substantially the same crystal orientation. The preferredcable comprises a plurality of fibers that are fused or sinteredtogether such that there is electrical connectivity between all thefibers. Alternatively, there is electrical connectivity between some,but not all of, the fibers of the cable.

The glass cladding for the cable preferably comprises an electricallyinsulating material comprising a binary, ternary or higher componentglass structure such as pyrex, borosilcate, aluminosilicate, quartz, andlead telluride-silicate. The thermoelectric material may be chosen fromthe group consisting of a metal, a semi-metal, an alloy and asemiconductor, such that the thermoelectric material exhibits electricalconnectivity and one or more of quantum confinement of carriers, reducedphysical defects such as vacancies and/or dislocations, reduced grainboundaries, single crystal formation, and favorable orientation ofgrains along a predetermined length of cable from several nanometers tokilometers. The ZT factor of the cable is preferably at least 0.5, morepreferably at least 1.5, most preferably at least 2.5.

3.0 APPLICATIONS OF NANOWIRE

3.1 Overview of Photolithography Based Devices

Conventional semiconductor devices such as field-effect-transistors(FETs), diodes and light-emitting diodes (LEDs), and photovoltaic cellsare typically manufactured using purely a photolithography process.FIGS. 10 and 11 illustrate two of such devices produced with aphotolithography process. FIG. 10 illustrates a metal-oxidesemiconductor FET (MOSFET) 1000. MOSFET 1000 is a N channel MOSFET thatincludes a P type well layer 1010 formed on a substrate (not shown). Ptype well layer 1010 is created by doping a previously charge-neutralsemiconductor material with a P-type dopant. Once well layer 1010 isformed, the two N-doped wells 1015 a and 1015 b are created. Wells 1015a-b are created by masking the surface of layer 1010 and leaving thesurface area where N wells 1015 a-b will be located unmasked. MOSFET1000 also includes an insulating layer 1020, and a gate 1025.

Gate 1025 may be made from metal or polysilicon (doped silicon), orother suitable material. Insulating layer 1020 is typically made from anoxide material. In MOSFET 1000, gate 1025 induces conduction between thetwo N regions 1015 a and 1015 b with the present its electric field.This typically occurs when the voltage at the gate is 0.6V above thesource.

FIG. 11 illustrates a semiconductor diode 1100, which is a simplesandwich of two layers of different materials. Diode 1100 includes an-doped layer 1110 and a p-doped layer 1120. Layers 1110 and 1120 aremated to form diode 1100. In a neutral state, layers 1110 and 1120 formsdepletion zone 1130, which is caused by the migration of electrons andholes from layer 1110 and layer 1120, respectively. Depletion zone 1130is neutral in charge. In an unbiased state, diode 1100 does not conductcurrent due to the present of depletion zone 1130. In a forward biasmode, diode 1100 allows electrons to flow from layer 1110 to layer 1120and holes to flow from layer 1120 to layer 1110. Diode 1100 is in aforward bias mode when layer 1110 is made more negative than layer 1120.Conversely, diode 1100 is in a reverse bias mode when layer 1110 is mademore positive than layer 1120. Current does not flow when diode 1100 isreverse biased.

Typically, optoelectronics devices such as LEDs are also made withsimilar lithographic processes. As will now be described, these commondevices (e.g., FETs, bi-polar transistors, diodes, LEDs, and logicgates) can be made using nanowires produced using methods in accordancewith various embodiments of the present invention.

3.2 Nanowire FETs

FIG. 12 illustrates an FET 1200 according to an embodiment of thepresent invention. FET 1200 includes a cable 1210, an oxide layer 1220,and a gate layer 1230. In producing FET 1200, cable 1210 can take theform of cable 60 (FIG. 3) or cable 65 (FIG. 6). As previously described,cable 60 is created using a plurality of monofibers 64 that are bundledtogether and then redrawn singly or multiple times until a desireddiameter is reached. The plurality of monofibers 64 in cable 60 arecomposed of the same thermoelectric material such as a n-doped materialor a p-doped material. In FET 1000, the middle portion of cable 1210 isp-doped and the two ends are n-doped. Gate 1230 is positioned such thatit is located over the p-doped portion of cable 1210. In this way, ann-channel inversion layer is created in the middle portion of cable 1210when gate 1230 is biased.

In FET 1200, oxide layer 1220 encompasses cable 1210. Oxide layer 1020acts as an insulating layer between cable 1210 and gate layer 1230. Inan embodiment, oxide layer 1220 is optional and is not required increating FET 1200. In this embodiment, the glass cladding of cable 1010can be made of an oxide composite material such as glass having leadoxide, tellurium dioxide, silicon dioxide or other suitable insulatingmaterials.

Similar to gate 825, gate layer 1230 may be made from metal,polysilicon, or other suitable material. Gate layer 1230 may be createdusing a coating process after the creation of cable 1210 and oxide layer1220. Gate layer 1230 may also be a prefabricated hollow cylinderwhereby cable 1210 may be inserted therein. Alternatively, cable 1210,oxide layer 1220, and layer 1230 can be produced simultaneously using adrawing process.

In an alternative embodiment of the present invention, cable 1210 of FET1200 comprises a single monofiber of thermoelectric material, similar tomonofiber 64 (FIG. 3). In this embodiment, the glass cladding thatsurrounds the single monofiber also acts as the insulating oxide layer.The drain and source are then created by introducing n or p dopants orimpurities to each end of cable 1210. N-type dopant is introduced ifcable 1210 is produced with p-type thermoelectric materials, whereasp-type dopant is introduced if cable 1210 is produced with n-typematerials. In this way, the middle portion of cable 1210 has theopposite thermoelectric composition than the two ends of cable 1210. Tocomplete the FET, gate layer 1230 is disposed on top of the middleportion of cable 1210.

FIG. 13 illustrates another FET 1300 according to an embodiment of thepresent invention. FET 1300 includes a fiber 1310, doped portions 1320 aand 1320 b, an oxide layer 1330, and a gate 1340. Fiber 1310 is a singlethermoelectric glass clad fiber, similar to monofiber 64. In analternative embodiment, fiber 1310 is a bundle of thermoelectric fiberssimilar to cable 60.

In FET 1300, fiber 1110 is made of p-doped thermoelectric materials. Tocreate the source and drain of the FET, each end of fiber 1310 is dopedwith n-type dopants. N-doped portion 1320 a acts as a gate, and N-dopedportion 1320 b acts as a drain. Portions 1320 a and 1320 b remainseparated by the middle portion of fiber 1310, which remains p-doped.

Oxide layer 1330 is the glass cladding of fiber 1310. As shown, oxidelayer 1330 is removed at each end of fiber 1310, but left intact in themiddle to provide a barrier between the gate and fiber 1310. The glasscladding layer above portions 1320 a-b may be removed through an etchingprocess. To complete FET 1300, gate 1340 is deposited on top of oxidelayer 1330.

In an alternative embodiment of the present invention, cable 1310 isn-doped and portions 1320 a-b are p-doped. In this embodiment, ap-channel enhancement MOSFET is produced.

3.3 Nanowire LEDs and Photovoltaic (PV) Cells

In general, all LEDs emit electromagnetic radiation. Whether theradiation is in the form of visible light depends on the frequency ofthe electromagnetic radiation. In its simplest form, LED is p-n junctiondiode. In general, radiation is produced when free electrons move tofrom a n-doped region to a p-doped region. This is called therecombination process. During the recombination process, electronsrelease energy in the form of photons or electromagnetic radiationswhenever they fall from a higher energy orbit to a lower energy orbit.However, most LEDs emit an invisible radiation. To make this radiationvisible, it is necessary to experiment with material make up of thesemiconductor layers and also with the band gap of the semiconductormaterials. The band gap of the semiconductor materials determines thefrequency of the emitted radiation as electrons fall to a lower orbit.

For LED applications, monofibers (e.g., monofiber 64 of FIG. 3) can madewith semiconductor materials having a wide band gap such as galliumphosphide, gallium arsenide phosephide, gallium nitrite, indium galliumnitrite, or other suitable semiconductor materials.

FIG. 14 illustrates an exemplary LED 1400 made with nanowire accordingto an embodiment of the present invention. LED 1400 includes ohmiccontacts 1410 a-b and cable portions 1420 and 1425. Ohmic contact 1410 ais disposed on one end of cable portion 1420 such that it makeselectrical contact with a plurality of monofibers 64 within cableportion 1420. In an embodiment, cable portion 1420 contains n-dopedmonofibers, and cable portion 1425 contains p-doped monofibers. Cableportion 1420 and cable portion 1425 are fused together at junction 1430,which forms one or more p-n junctions at junction 1430. To complete theLED, another ohmic contact 1410 b is provided at the end of cableportion 1425. Once the circuit is completed by electrically couplingohmic contacts 1410 a and 1410 b, electrons may migrate from cableportion 1420 to cable portion 65, or vice versa, and produce light as aby-product. Cable portions 1420 and 1425 may be made using a processsimilar to that described with respect to FIGS. 3-6.

FIG. 15 illustrates a nanowire PV cell 1500 according to an embodimentof the present invention. PV cell 1500 includes cable portions 1510 and1520. Cable portion 1510 is made from n-type thermoelectric material,and cable portion 1520 is made from p-type materials. Both cableportions 1510 and 1520 are manufactured using processes similar to themanufacturing processes with respect to FIGS. 3-6. Similar to a diode,portion 1530 forms neutral state 1530 where there is no current flow.However, when cable portion 1510 is energized by photons, neutral state1530 is disrupted. In the disrupted state, electrons from portion 1510are induced to migrate to portion 1520 so equilibrium may be reached. Tocomplete the PV cell, an external current path is provided betweenportions 1510 and 1520.

Thus, it is seen that a thermoelectric device with enhanced physicalperformance and properties may be on account of one or more of thefollowing properties or effects: quantum confinement of carriers, lessphysical defects such as vacancies and/or dislocations, grain boundariesis reduced or eliminated, single crystal formation, and favorableorientation of grains. One skilled in the art will appreciate that thepresent invention can be practiced by other than the various embodimentsand preferred embodiments, which are presented in this description forpurposes of illustration and not of limitation, and the presentinvention is limited only by the claims that follow. It is noted thatequivalents for the particular embodiments discussed in this descriptionmay practice the invention as well.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not of limitation. Likewise, the various diagrams maydepict an example architectural or other configuration for theinvention, which is done to aid in understanding the features andfunctionality that may be included in the invention. The invention isnot restricted to the illustrated example architectures orconfigurations, but the desired features may be implemented using avariety of alternative architectures and configurations. Indeed, it willbe apparent to one of skill in the art how alternative functional,logical or physical partitioning and configurations may be implementedto implement the desired features of the present invention. Also, amultitude of different constituent module names other than thosedepicted herein may be applied to the various partitions. Additionally,with regard to flow diagrams, operational descriptions and methodclaims, the order in which the steps are presented herein shall notmandate that various embodiments be implemented to perform the recitedfunctionality in the same order unless the context dictates otherwise.

Although the invention is described above in terms of various exemplaryembodiments and implementations, it should be understood that thevarious features, aspects and functionality described in one or more ofthe individual embodiments are not limited in their applicability to theparticular embodiment with which they are described, but instead may beapplied, alone or in various combinations, to one or more of the otherembodiments of the invention, whether or not such embodiments aredescribed and whether or not such features are presented as being a partof a described embodiment. Thus the breadth and scope of the presentinvention should not be limited by any of the above-described exemplaryembodiments.

Terms and phrases used in this document, and variations thereof, unlessotherwise expressly stated, should be construed as open ended as opposedto limiting. As examples of the foregoing: the term “including” shouldbe read as meaning “including, without limitation” or the like; the term“example” is used to provide exemplary instances of the item indiscussion, not an exhaustive or limiting list thereof; the terms “a” or“an” should be read as meaning “at least one,” “one or more” or thelike; and adjectives such as “conventional,” “traditional,” “normal,”“standard,” “known” and terms of similar meaning should not be construedas limiting the item described to a given time period or to an itemavailable as of a given time, but instead should be read to encompassconventional, traditional, normal, or standard technologies that may beavailable or known now or at any time in the future. Likewise, wherethis document refers to technologies that would be apparent or known toone of ordinary skill in the art, such technologies encompass thoseapparent or known to the skilled artisan now or at any time in thefuture.

A group of items linked with the conjunction “and” should not be read asrequiring that each and every one of those items be present in thegrouping, but rather should be read as “and/or” unless expressly statedotherwise. Similarly, a group of items linked with the conjunction “or”should not be read as requiring mutual exclusivity among that group, butrather should also be read as “and/or” unless expressly statedotherwise. Furthermore, although items, elements or components of theinvention may be described or claimed in the singular, the plural iscontemplated to be within the scope thereof unless limitation to thesingular is explicitly stated.

The presence of broadening words and phrases such as “one or more,” “atleast,” “but not limited to” or other like phrases in some instancesshall not be read to mean that the narrower case is intended or requiredin instances where such broadening phrases may be absent. The use of theterm “module” does not imply that the components or functionalitydescribed or claimed as part of the module are all configured in acommon package. Indeed, any or all of the various components of amodule, whether control logic or other components, may be combined in asingle package or separately maintained and may further be distributedacross multiple locations.

Additionally, the various embodiments set forth herein are described interms of exemplary block diagrams, flow charts and other illustrations.As will become apparent to one of ordinary skill in the art afterreading this document, the illustrated embodiments and their variousalternatives may be implemented without confinement to the illustratedexamples. For example, block diagrams and their accompanying descriptionshould not be construed as mandating a particular architecture orconfiguration.

1. A field effect transistor device, comprising: at least onesemiconductor fiber comprising a channel region of a first conductivitytype located between a source region and a drain region of a secondconductivity type; a glass gate insulating layer located on the channelregion; and a gate electrode located adjacent to the glass gateinsulating layer, wherein the glass gate insulating layer surrounds thechannel region in the at least one semiconductor fiber and the gateelectrode comprises a cylinder which surrounds the glass gate insulatinglayer.
 2. The device of claim 1, wherein an inversion region is createdin the channel region when the gate electrode is biased.
 3. The deviceof claim 1, wherein the glass comprises pyrex glass, vycor glass,borosilcate glass, aluminosilicate glass, quartz glass, leadtelluride-silicate glass, silicon oxide glass, lead oxide glass,tellurium dioxide glass, or combinations thereof.
 4. The device of claim1, wherein the at least one semiconductor fiber comprises a single fiberand the entire channel region of the transistor is located in the singlefiber.
 5. The device of claim 1, wherein the at least one semiconductorfiber comprises a cable containing a plurality of glass cladsemiconductor fibers and the channel region of the transistor is locatedin the plurality of glass clad semiconductor fibers.
 6. The device ofclaim 1, wherein the source region and the drain region are not coveredby the glass gate insulating layer.
 7. The device of claim 1, furthercomprising a first conductor coupled to the source region and a secondconductor coupled to the drain region.
 8. A field effect transistordevice, comprising: at least one semiconductor fiber comprising achannel region of a first conductivity type located between a sourceregion and a drain region of a second conductivity type; a glass gateinsulating layer located on the channel region; and a gate electrodelocated adjacent to the glass gate insulating layer, wherein the atleast one semiconductor fiber comprises a single fiber and the entirechannel region of the transistor is located in the single fiber.
 9. Thedevice of claim 8, wherein an inversion region is created in the channelregion when the gate electrode is biased.
 10. The device of claim 8,wherein the glass comprises pyrex glass, vycor glass, borosilcate glass,aluminosilicate glass, quartz glass, lead telluride-silicate glass,silicon oxide glass, lead oxide glass, tellurium dioxide glass, orcombinations thereof.
 11. The device of claim 8, wherein the glass gateinsulating layer is located over only one side of the channel region inthe at least one semiconductor fiber and the gate electrode is locatedover glass gate insulating layer.
 12. The device of claim 8, wherein thesource region and the drain region are not covered by the glass gateinsulating layer.
 13. The device of claim 8, further comprising a firstconductor coupled to the source region and a second conductor coupled tothe drain region.
 14. A field effect transistor device, comprising: atleast one semiconductor fiber comprising a channel region of a firstconductivity type located between a source region and a drain region ofa second conductivity type; a glass gate insulating layer located on thechannel region; and a gate electrode located adjacent to the glass gateinsulating layer, wherein the at least one semiconductor fiber comprisesa cable containing a plurality of glass clad semiconductor fibers andthe channel region of the transistor is located in the plurality ofglass clad semiconductor fibers.
 15. The device of claim 14, wherein aninversion region is created in the channel region when the gateelectrode is biased.
 16. The device of claim 14, wherein the glasscomprises pyrex glass, vycor glass, borosilcate glass, aluminosilicateglass, quartz glass, lead telluride-silicate glass, silicon oxide glass,lead oxide glass, tellurium dioxide glass, or combinations thereof. 17.The device of claim 14, wherein the glass gate insulating layer islocated over only one side of the channel region in the at least onesemiconductor fiber and the gate electrode is located over glass gateinsulating layer.
 18. The device of claim 14, wherein the source regionand the drain region are not covered by the glass gate insulating layer.19. The device of claim 14, further comprising a first conductor coupledto the source region and a second conductor coupled to the drain region.